1. Field of the Invention
The present invention relates to a polymer battery pack and a method for manufacturing the same, and more particularly to a polymer battery pack having reinforced external strength and increased capacity and a method for manufacturing the same.
2. Description of the Prior Art
In general, a polymer battery pack includes a core pack having a protective circuit module connected to a pouch-type bare cell and a plastic case having all edges thermally bonded to it by ultrasonic waves with the core pack contained therein. The conventional, pouch-type bare cell refers to a lithium polymer battery having a polymer electrolyte and an electrode assembly, which includes a positive electrode, a separator, and a negative electrode, contained in a pouch made of cast polypropylene (CPP), aluminum, nylon, or polyethylene terephthalate (PET). The polymer battery pack and lithium polymer battery should be distinguished from battery packs and lithium ion batteries using a liquid electrolyte.
The polymer battery pack has a problem in that it is easily damaged by external impact and has degraded reliability, because both the pouch constituting a bare cell and the plastic case enclosing it have poor strength. In particular, the pouch is made of foil-type aluminum and the plastic case enclosing it has a small thickness. As a result, the polymer battery pack is easily deformed by external forces and is easily penetrated by sharp nails or needles. If such deformation or penetration occurs, the polymer battery pack may smoke, catch fire, or explode due to a short circuit.
The polymer battery pack has a rib space on each edge so that the plastic case can be welded thereto by ultrasonic waves. Such space occupies at least 0.8 mm and reduces the size of the core pack and bare cell accordingly, which is contained in the polymer battery pack. This results in decreased capacity. The fact that the core pack contained in the plastic case is substantially smaller than the plastic case makes it very difficult to contain a large-capacity core pack in the plastic case. In practice, conventional polymer battery packs typically cannot contain a core pack having a capacity of about 680 mAh or larger.